A circadian rhythm (CR) is a roughly 24-hour cycle in the physiological processes of living beings, including plants, animals, fungi, and cyanobacteria. In a strict sense, circadian rhythms are endogenously generated, although they can be modulated by external cues such as sunlight and temperature. Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including human beings. There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle.
A CR state is a state reached in the CR cycle at a given point in time. For example, being asleep is a CR state when the CR pattern suggests that the organism is asleep. Many other CR states similarly exists, e.g., being awake, being hungry, being agitated, being active, being lethargic, etc.
Humans transition from one CR state to another over a period of time. A micro circadian rhythm (MCR) comprises microscopic or minute changes in the CR that are indicative of a change in the CR. Particularly, MCRs are indicative of an upcoming change from one CR state to another CR state.